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Association of the PPAR-γ Gene with Altered Glucose Levels and Psychosis Profile in Schizophrenia Patients Exposed to Antipsychotics Yun-Ru Liu1*, Tsung-Ming Hu2*, Tsuo-Hung Lan3,4,5, Hsien-Jane Chiu3,6,7, Yung-Han Chang8, Shuo-Fei Chen9,10, Yen-Hsin Yu11, Cheng-Chung Chen12, and El-Wui Loh12 Office of Research and Development, Taipei Medical University, Taipei, Taiwan Yuli Veterans Hospital, Yuli Township, Hualian County, Taiwan 3 Faculty of Medicine, National Yang Ming University, Taipei, Taiwan 4 Department of Psychiatry, Taichung Veterans General Hospital, Taichung, Taiwan 5 Center for Neuropsychiatric Research, National Health Research Institutes, Miaoli County, Taiwan 6 Chung Hwa University of Medical Technology, Tainan, Taiwan 7 Department of Psychiatry, Min-Sheng General Hospital, Taoyuan City, Taiwan 8 Institute of Public Health and Department of Public Health, National Yang Ming University, Taipei, Taiwan 9 Department of Health Care and Social Work, Yu Da University of Science and Technology, Chao-chiao Township, Miaoli County, Taiwan 10 Institute of Food Science and Technology, National Taiwan University, Taipei, Taiwan 11 Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan 12 Kaohsiung Municipal Kai-Syuan Psychiatric Hospital, Kaohsiung, Taiwan 1 2
ObjectiveaaMetabolic abnormalities, e.g., diabetes, are common among schizophrenia patients. Peroxisome proliferator activated
receptor-γ (PPAR-γ) regulates glucose/lipid metabolisms, and schizophrenia like syndrome may be induced by actions involving retinoid X receptor-α/PPAR-γ heterodimers. We examined a possible role of the PPAR-γ gene in metabolic traits and psychosis profile in schizophrenia patients exposed to antipsychotics. MethodsaaSingle nucleotide polymorphisms (SNPs) of the PPAR-γ gene and a serial of metabolic traits were determined in 394 schizophrenia patients, among which 372 were rated with Positive and Negative Syndrome Scale (PANSS). ResultsaaSNP-10, -12, -18, -19, -20 and -26 were associated with glycated hemoglobin (HbA1c) whereas SNP-18, -19, -20 and -26 were associated with fasting plasma glucose (FPG). While SNP-23 was associated with triglycerides, no associations were identified between the other SNPs and lipids. Further haplotype analysis demonstrated an association between the PPAR-γ gene and psychosis profile. ConclusionaaOur study suggests a role of the PPAR-γ gene in altered glucose levels and psychosis profile in schizophrenia patients exposed to antipsychotics. Although the Pro12Ala at exon B has been concerned an essential variant in the development of obesity, the lack of association of the variant with metabolic traits in this study should not be treated as impossibility or a proof of error because other factors, e.g., genes regulated by PPAR-γ, may have complicated the development of metabolic abnormalities. Whether the PPAR-γ gene modifies the risk of metabolic abnormalities or psychosis, or causes metabolic abnormalities that lead to psychosis, remains to be Psychiatry Investig 2014;11(2):179-185 examined. Key WordsaaSchizophrenia, Psychosis, Glucose, PPAR-γ gene.
INTRODUCTION Metabolic abnormalities, e.g., DM, are common among
schizophrenia patients. DM may be induced by antipsychotics medications,1 or may occur before the antipsychotics exposure in a considerable number of schizophrenia patients.2 Positive
Received: February 10, 2013 Revised: August 5, 2013 Accepted: September 7, 2013 Available online: April 11, 2014 Correspondence: El-Wui Loh, PhD Kaohsiung Municipal Kai-Syuan Psychiatric Hospital, No.130, Kaisyuan 2nd Rd., Lingya Dist., Kaohsiung City 80276, Taiwan (R.O.C.) Tel: +886-7-751-3171, Fax: +886-7-771-2494, E-mail: [email protected]
*These authors contributed equally to this study. cc This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
syndrome of most schizophrenia patients can be relieved to some extents by antipsychotic treatments, but this is not the case for negative syndrome,3,4 suggesting that schizophrenia patients with severe negative syndrome may represent a subgroup with distinct biological features. Peroxisome proliferator-activated receptors (PPARs) belong to the superfamily of nuclear receptors (NRs), and play a central role in the transcriptional control of glucose and lipid regulation. The agonism of NRs has been used as a molecular strategy for treating diabetes and hyperglycemia.5 Three different human PPAR subtypes, namely PPAR-α, PPAR-β (also known as PPAR-δ) and PPAR-γ,6,7 have been identified. PPAR-γ is the most frequently studied NR, and is involved in the control of energy balance and lipid and glucose homeostasis.8 Several PPAR-γ gene knockout studies in mice have demonstrated glucose and lipid metabolism cross-talks between adipose tissue, muscle and liver, suggesting that PPAR-γ is important for retaining normal insulin sensitivity and whole-body glucose and lipid homeostasis.9,10 Also, genomewide association and association studies have indicated a genetic contribution of the PPAR-γ gene in the development of type 2 DM and metabolic traits.11,12 The activation of PPAR-γ mediates anti-inflammation in the cardiovascular system and nervous system.13 PPAR-γ forms a heterodimer complex with retinoid X receptor-α (RXRα), which then binds to peroxisome proliferator response elements (PPREs) within the promoters of PPAR-γtargeted genes.14,15 Retinoic acid receptors (RARs) are present in all parts of the cranial region, and delivery of retinoids is exquisitely controlled throughout the embryonic and fetal development.16 RARs act either alone or together with the heterodimeric partners. An in vitro experiment in adult human keratinocytes showed that endogenous retinoic acid RARRXR heterodimers are the major functional forms that regulate the retinoid-responsive elements,17 suggesting that an accurate regulation between PPAR-γ, RAR and RXR is needed to ensure a normal brain development and function. Because retinoid toxicity or deficit produces symptoms resembling schizophrenia,16 it is reasonable to deduce that genetic variants in the PPAR genes may affect the functioning of retinoid cascade and, thus, have profound implications in schizophrenia. The objective of the study was to investigate a possible role of the PPAR-γ gene in metabolic traits and psychosis profile in schizophrenia patients in Taiwan.
This study was approved by the Institutional Review Board of Yu-Li Hospital, Department of Health, Taiwan, file number
Psychiatry Investig 2014;11(2):179-185
YLH-93001. A total of 401 subjects (300 males and 101 females) meeting DSMIV criteria of schizophrenia and who had been exposed to antipsychotics treatment for more than 2 years, were recruited. None of the patients were exposed to psychiatric therapeutics other than antipsychotics except hypnotics when medically required. Medication for physical health problems was intervened in any form during the study period. The mean age of the study population was 49.3±9.9, ranging from 21 to 84 years. All eligible patients signed the informed consent form for blood donation and genetic analysis. At last, 394 good satisfactory DNA samples were obtained and used for genotyping. Psychosis profiles were evaluated using the Positive and Negative Syndrome Scale (PANSS) Taiwan Chinese version, which includes subscales of positive syndrome, negative syndrome and general psychopathology.18 Three hundred and seventy two out of the 401 schizophrenia patients were successfully assessed using PANSS by boardcertified psychiatrists. None of the patients were rated during acute psychosis. All patients examined in this study resided in a commodious environment.
BMI, waistline, fasting plasma glucose (FPG), glycated hemoglobin (HbA1c), total cholesterol (TC), triglycerides (TGA), low density lipoprotein cholesterol (LDL), high density lipoprotein cholesterol (HDL), were measured on October 2004. Details of measurement of the indexes are summarized in supplement file.
The human PPAR-γ gene is located on chromosomal region 3p25.19 At least 7 human PPAR-γ mRNA splice variants have been found, each consists of exons 1 through 6 consecutively.20 The PPAR-γ protein exists in 2 isoforms-PPAR-γ1 with 477 amino acids and PPAR-γ2 with 505 amino acids. The PPAR-γ1 mRNAs are coded by 8 exons (A1, A2, 1, 2, 3, 4, 5, and 6), among which exon A1 and A2 are untranslated. The PPAR-γ2 mRNAs are encoded by 7 exons (exon B, 1, 2, 3, 4, 5, and 6), among which the additional 28 amino acids are encoded by exon B.21 Information of single nucleotide polymorphisms (SNPs) of the PPAR-γ gene in Han Chinese population (Beijing, China) and Japanese population (Tokyo, Japan) were retrieved from the HapMap database (phase II, 7 Jan 2007, http://hapmap. ncbi.nlm.nih.gov). Twenty TaqSNPs with minor allele frequency (MAF) ≥0.03 were selected using the Hapmap Tagger Program; 9 coding SNPs available during the research period were selected from dbSNP (Build 125) for genotyping. Detailed information of the SNPs, including chromosomal position, nucleotide location, exonic or intronic (based on PPAR-
YR Liu et al.
γ2 mRNA and protein encoded by exon B, 1, 2, 3, 4, 5, and 6), allelic variants and amino acid changes, are summarized in supplement file. The Sequenom MassARRAY® iPLEX Gold platform (Sequenom Inc., San Diego, CA, USA) and calling software Typer were used for genotyping and signal analysis.
mutation tests randomly assigned the identification labels to the patients (each possessed a specific haplotype), creating a scenario where the dependent variable (i.e., PANSS) was not related to the PPAR-γ gene. The SAS program was used for the GLM statistical analysis and permutations.
SNPs not deviated from the Hardy-Weinberg equilibrium and ≥0.03 were analyzed using the HaploviewTM program 4.1 (http://www.broadinstitute.org/scientific-community/science/programs/medical-and-population-genetics/haploview/ haploview). General linear model (GLM) was used to estimate the contribution of each SNP, age, gender, the use of typical antipsychotics, and the use of atypical antipsychotics on metabolic indexes by applying the enter method. SNPs that possibly confer functionality or associated with genetic variants with functionality (i.e., SNPs significantly associated with metabolic indexes),22 were used to evaluate a role of the PPAR-γ gene in psychosis profile. The additive and dominant genetic effects of each haplotype on PANSS were tested against the other haplotypes (i.e., other haplotypes were merged and considered as one haplotype) in the same GLM with age, gender, the use of typical antipsychotics, and the use of atypical antipsychotics included. The code for additive effect (0, 1 or 2) in the data sheet was the frequency of the haplotype of interests. For dominant effects, the code was 1 when one haplotype of interests existed, and 0 when no haplotype of interest existed. After each haplotype was examined, those significantly contributed to PANSS either through additive or dominant effects, were further permutated with 10,000 iterations. The per-
Among the 29 SNPs we examined, genotype distribution of 2 SNPs significantly deviated from the Hardy-Weinberg equilibrium and 9 SNPs had MAF
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